Turbine shroud arrangement for a turbine system and method of controlling a turbine shroud arrangement

ABSTRACT

A turbine shroud arrangement for a turbine system includes a first region of a tip shroud, the first region disposed in close proximity to an adjacent tip shroud. Also included is a second region of the tip shroud, the second region disposed in close proximity to the adjacent tip shroud, the second region comprising a temperature sensitive material configured to engage the second region and the adjacent tip shroud in contact over a first operating condition of the turbine system and configured to provide a second region gap over a second operating condition of the turbine system.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to turbine systems, and moreparticularly to turbine bucket tip shroud arrangements, as well as amethod of controlling a turbine bucket tip shroud arrangement.

Turbine systems employ a number of rotating components or assemblies,such as compressor stages and turbine stages that rotate at high speedwhen the turbine is in operation, for example. In general, a stageincludes a plurality of free-floating blades that extend radiallyoutward from a central hub. Some blades include a tip shroud that limitsvibration within a stage and provides sealing to increase efficiency ofthe overall system. The shroud is typically positioned at a tip portionof the blade, a mid-portion of the blade or at both the mid portion andthe tip portion of the blade. The shrouds are designed such that thefree-floating blades interlock to form an integral rotating memberduring operation.

Prior to rotation of the free-floating blades, a gap between contactsurfaces of the shrouds is present. The distance of the gap determineshow early an interlock of the shrouds occurs upon startup of the turbinesystem. Too large of a gap inefficiently delays the locking speed,thereby resulting in resonance, for example. Too small of a gap resultsin undesirable effects at high speed operation of the turbine system.Such effects include high stresses imposed on the turbine bucket due toincreased transfer of forces between the contacting shrouds, forexample. Therefore, current efforts to beneficially reduce the gap toprovide an early interlock to address potential low speed aeromechanicsissues are mitigated by the detrimental effects on tip shroud life thatoccur at steady state operating conditions.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a turbine shroud arrangementfor a turbine system includes a first region of a tip shroud, the firstregion disposed in close proximity to an adjacent tip shroud. Alsoincluded is a second region of the tip shroud, the second regiondisposed in close proximity to the adjacent tip shroud, the secondregion comprising a temperature sensitive material configured to engagethe second region and the adjacent tip shroud in contact over a firstoperating condition of the turbine system and configured to provide asecond region gap over a second operating condition of the turbinesystem.

According to another aspect of the invention, a turbine shroudarrangement for a turbine system includes a first region of a tipshroud, the first region disposed in close proximity to an adjacentfirst region of an adjacent tip shroud. Also included is a second regionof the tip shroud, the second region disposed in close proximity to anadjacent second region of the adjacent tip shroud. Further included is atemperature sensitive material disposed proximate the second region, thetemperature sensitive material comprising a first volume during a firstoperating condition of the turbine system and a second volume during asecond operating condition of the turbine system, wherein the secondvolume is less than the first volume.

According to yet another aspect of the invention, a method ofcontrolling a turbine shroud arrangement is provided. The methodincludes disposing a first region gap between a first region of a tipshroud and an adjacent tip shroud. Also included is reducing a secondregion gap disposed between a second region of the tip shroud and theadjacent tip shroud by depositing a temperature sensitive materialproximate the second region. Further included is engaging the secondregion with the adjacent tip shroud during a first operating conditionof a turbine system and providing the second region gap during a secondoperating condition of the turbine system. Yet further included isproviding the first region gap during the first operating condition andreducing the first region gap to engage the first region with theadjacent tip shroud during the second operating condition.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view of a turbine system;

FIG. 2 is a partial perspective view of a turbine stage of the turbinesystem;

FIG. 3 is a top plan view of a turbine bucket tip shroud arrangementhaving a first region and a second region;

FIG. 4 is a schematic view of the first region and the second region ina first operating condition;

FIG. 5 is a schematic view of the first region and the second region ina second operating condition; and

FIG. 6 is a flow diagram illustrating a method of controlling theturbine bucket tip shroud arrangement.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a turbine system, shown in the form of a gasturbine engine, constructed in accordance with an exemplary embodimentof the present invention, is indicated generally at 10. The turbinesystem 10 includes a compressor 12 and a plurality of combustorassemblies arranged in a can annular array, one of which is indicated at14. As shown, the combustor assembly 14 includes an endcover assembly 16that seals, and at least partially defines, a combustion chamber 18. Aplurality of nozzles 20-22 are supported by the endcover assembly 16 andextend into the combustion chamber 18. The nozzles 20-22 receive fuelthrough a common fuel inlet (not shown) and compressed air from thecompressor 12. The fuel and compressed air are passed into thecombustion chamber 18 and ignited to form a high temperature, highpressure combustion product or air stream that is used to drive aturbine 24. The turbine 24 includes a plurality of stages 26-28 that areoperationally connected to the compressor 12 through acompressor/turbine shaft 30 (also referred to as a rotor).

In operation, air flows into the compressor 12 and is compressed into ahigh pressure gas. The high pressure gas is supplied to the combustorassembly 14 and mixed with fuel, for example process gas and/orsynthetic gas (syngas), in the combustion chamber 18. The fuel/air orcombustible mixture ignites to form a high pressure, high temperaturecombustion gas stream. Alternatively, the combustor assembly 14 cancombust fuels that include, but are not limited to, natural gas and/orfuel oil. In any event, the combustor assembly 14 channels thecombustion gas stream to the turbine 24 which converts thermal energy tomechanical, rotational energy.

At this point, it should be understood that each of the plurality ofstages 26-28 is similarly formed, thus reference will be made to FIG. 2in describing stage 26 constructed in accordance with an exemplaryembodiment of the present invention with an understanding that theremaining stages, i.e., stages 27 and 28, have corresponding structure.Also, it should be understood that the present invention could beemployed in stages in the compressor 12 or other rotating assembliesthat require wear and/or impact resistant surfaces. In any event, thestage 26 is shown to include a plurality of rotating members, such as anairfoil 32, which each extend radially outward from a central hub 34having an axial centerline 35. The airfoil 32 is rotatable about theaxial centerline 35 of the central hub 34 and includes a base portion 36and a tip portion 38.

A tip shroud 50 covers the tip portion 38 of the airfoil 32. The tipshroud 50 is designed to receive, or nest with, tip shrouds on adjacentrotating members in order to form a continuous ring that extendscircumferentially about the stage 26. The continuous ring creates anouter flow path boundary that reduces gas path air leakage over topportions (not separately labeled) of the stage 26, so as to increasestage efficiency and overall turbine performance. In the exemplaryembodiment shown, during high or operational speeds, adjacent airfoilsinterlock through the tip shroud 50 of each respective airfoil by virtueof centrifugal forces created by the operation of the turbine 24.

Referring now to FIGS. 3-5, the tip shroud 50 is illustrated in greaterdetail and is in close proximity with an adjacent tip shroud 52. The tipshroud 50 includes a first region 54 and a second region 56, eachconfigured to engage the adjacent tip shroud 52 at various operatingconditions of the turbine system 10. Specifically, the first region 54engages an adjacent first region 58 of the adjacent tip shroud 52, whilethe second region 56 engages an adjacent second region 60 of theadjacent tip shroud 52. At various operating conditions of the turbinesystem 10, which will be described in detail below, a first region gap62 is present between the tip shroud 50 and the adjacent tip shroud 52,and more particularly between the first region 54 and the adjacent firstregion 58. Similarly, at various operating conditions, a second regiongap 64 is present between the tip shroud 50 and the adjacent tip shroud52, and more particularly between the second region 56 and the adjacentsecond region 60.

To achieve an early interlock of the tip shroud 50 and the adjacent tipshroud 52, at least one of the second region 56 and the adjacent secondregion 60, but typically both the second region 56 and the adjacentsecond region 60, include a thermally sensitive material 70. Thethermally sensitive material 70 is configured to dimensionally adjust inresponse to temperature variation. In one embodiment, the thermallysensitive material 70 is a negative thermal expansion material definedby having a negative coefficient of thermal expansion, such that thematerial contracts in response to increased temperature exposure, ratherthan expanding. It is to be appreciated that any material having anegative coefficient of thermal expansion may be suitable for inclusionwith the second region 56 and the adjacent second region 60. Examples ofsuch materials include zircon, zirconium tungstate and A₂(MO₄)₃compounds. In another embodiment, the thermally sensitive material 70comprises a shape memory alloy configured to be manipulated in responseto thermal changes. Examples of suitable shape memory alloys includesmaterials comprising a titanium nickel (TiNi) alloy, palladium (Pd),gold (Au) and zirconium (Zr), among others. Although the second region56 has been described as a single region, it is to be appreciated that aplurality of regions may include the thermally sensitive material 70 forestablishing contact during operating conditions similar to the secondregion 56 and the adjacent second region 60. One such illustrativeregion is shown as a third region 68 and an adjacent third region 69,for example. For clarity of description, the second region 56 and theadjacent second region 60 will be described herein, with theunderstanding that additional similarly constructed and positionedregions may be present.

Forming at least a portion of the second region 56 and the adjacentsecond region 60 with the thermally sensitive material 70 advantageouslyallows for an early interlock between the tip shroud 50 and the adjacenttip shroud 52 during a first operating condition (FIG. 4) correspondingto a first turbine speed range. The first turbine speed range may varydepending on the application, but in one embodiment the first turbinespeed range is from about 0% to about 50% of a maximum turbine operatingspeed. Operation over this range corresponds to a cooler operatingenvironment for the tip shroud 50 relative to a second operatingcondition (FIG. 5) corresponding to a second turbine speed range.Similar to the first turbine speed range, the second turbine speed rangemay vary depending on the application, but in one embodiment the secondturbine speed range is from about 30% to about 100% of the maximumturbine operating speed. The maximum turbine operating speed will varybased on the particular application as well. It can be appreciated thatduring the first operating condition, the thermally sensitive material70, and therefore the second region 56, is disposed at a first positionand is of a first dimension, such as a volume. As the operatingenvironment increases in temperature, the position and/or the dimensionsof the second region 56 changes. Specifically, the thermally sensitivematerial 70 contracts and/or retracts from the adjacent second region60, thereby forming the second region gap 64 at the transition to thesecond operating condition. As noted above, the adjacent second region60 may include the thermally sensitive material 70, such that it maysimilarly contract or retract from the second region 56. In other words,the second region 56 and the adjacent second region 60 may contract froma first volume to a smaller, second volume or may simply retract fromone another as the temperature increases.

In the first operating condition, the first region 54 and the adjacentfirst region 58 are spaced from one another, thereby defining the firstregion gap 62. To alleviate stresses imposed on the tip shroud 50, theadjacent tip shroud 52 and the airfoil 32, the first region 54 and theadjacent first region 58 are not engaged into contact until the secondoperating condition is satisfied. Stress reduction is achieved byavoiding early and continuous contact that otherwise may be employed tomeet rapid interlock goals. Rather, early interlock during the firstoperating condition is achieved by engagement of the second region 56and the adjacent second region 60 and subsequent engagement of the firstregion 54 and the adjacent first region 58 during the second operatingcondition. During the second operating condition, the first region 54and the adjacent first region 58 may thermally expand and shift due totemperature increase and increased centrifugal forces, respectively.Such responses increase the stresses noted above, however, thesestresses are mitigated by the delayed engagement of the first region 54and the adjacent first region 58. As described above, the second region56 and the adjacent second region 60 are thermally manipulated toestablish the second region gap 64 during the second operatingcondition, thereby reducing any stresses that may otherwise be imposedduring increased temperature and centrifugal force application duringthe second operating condition.

The first region gap 62 and the second region gap 64 both may vary indimension depending on the application, but in one embodiment the firstregion gap 62 may range from about 5 mils (about 0.005″ or about 0.127mm) to about 50 mils (about 0.050″ or about 1.27 mm) In yet anotherembodiment, the first region gap 62 is about 20 mils (about 0.020″ orabout 0.508 mm) The second region gap 64 may range from about 5 mils(about 0.005″ or about 0.127 mm) to about 75 mils (about 0.075″ or about1.905 mm) In yet another embodiment, the second region gap 64 rangesfrom about 20 mils (about 0.020″ or about 0.508 mm) to about 50 mils(about 0.05″ to about 1.27 mm) The preceding description of dimensionsof the first gap region 62 and the second gap region 64 is merelyexemplary and is not intended to be limiting of various other suitabledimensions. The first region gap 62 and the second region gap 64 aredimensionally selected based on a desirable early interlock of the tipshroud 50 and the adjacent tip shroud 52 upon operation of the turbinesystem 10 and rotation of the airfoil 32.

It is contemplated that the second region 56 and the adjacent secondregion 60 are coated or integrally formed with the tip shroud 50 and theadjacent tip shroud 52, respectively. The second region 56 and theadjacent second region 60 may be formed of one or more compositionlayers that typically include a fraction of the thermally sensitivematerial 70 and a fraction of a wear resistant material. In anembodiment having a plurality of composition layers, it is to beappreciated that distinct volume and/or weight fractions of thethermally sensitive material 70 may be present in the plurality ofcomposition layers. In one embodiment, the fraction of the thermallysensitive material 70 progressively increases in each layer, relative tomoving away from a base metal of the tip shroud 50 and the adjacent tipshroud 52. It is to be appreciated that each of the plurality ofcomposition layers may vary in thickness from one another and maycomprise the thermally sensitive material 70 in a fraction ranging fromabout 0% to about 100%.

The second region 56 and/or the adjacent second region 60, whether asingle layer or a plurality of composition layers, may be deposited orintegrated with the tip shroud 50 and the adjacent tip shroud 52 in anumber of application processes. Examples of such processes includebrazing, welding, laser cladding, cold spraying and a plasma transferredarc (PTA) process. The preceding list is merely illustrative and is notintended to be limiting of numerous other suitable applicationprocedures.

As illustrated in the flow diagram of FIG. 6, and with reference toFIGS. 1-5, a method of controlling a turbine shroud arrangement 100 isalso provided. The turbine system 10, as well as the tip shroud 50 andthe second region 56, have been previously described and specificstructural components need not be described in further detail. Themethod of controlling a turbine shroud arrangement 100 includesdisposing a first region gap between a first region of a tip shroud andan adjacent tip shroud 102. A second region gap disposed between asecond region of the tip shroud and the adjacent tip shroud is reducedby depositing a temperature sensitive material proximate the secondregion 104. The second region is engaged with the adjacent tip shroudduring a first operating condition of the turbine system 106, therebyproviding the second region gap during a second operating condition ofthe turbine system. The first region gap is provided during the firstoperating condition 108, thereby reducing the first region gap to engagethe first region with the adjacent tip shroud during the secondoperating condition.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A turbine shroud arrangement for a turbine system comprising: a firstregion of a tip shroud, the first region disposed in close proximity toan adjacent tip shroud; and a second region of the tip shroud, thesecond region disposed in close proximity to the adjacent tip shroud,the second region comprising a temperature sensitive material configuredto engage the second region and the adjacent tip shroud in contact overa first operating condition of the turbine system and configured toprovide a second region gap over a second operating condition of theturbine system.
 2. The turbine shroud arrangement of claim 1, whereinthe temperature sensitive material comprises a negative thermalexpansion material.
 3. The turbine shroud arrangement of claim 1,wherein the temperature sensitive material comprises a shape memoryalloy.
 4. The turbine shroud arrangement of claim 1, further comprisinga first region gap disposed between the first region and the adjacenttip shroud during the first operating condition.
 5. The turbine shroudarrangement of claim 4, wherein the first region and the adjacent tipshroud are in contact during the second operating condition.
 6. Theturbine shroud arrangement of claim 1, further comprising an adjacentsecond region of the adjacent tip shroud, the adjacent second regioncomprising the temperature sensitive material.
 7. The turbine shroudarrangement of claim 1, wherein the first operating condition comprisesa turbine operating speed range from about 0% to about 50% of a maximumspeed of the turbine system.
 8. The turbine shroud arrangement of claim1, wherein the second operating condition comprises a turbine operatingspeed range from about 30% to about 100% of a maximum speed of theturbine system.
 9. A turbine shroud arrangement for a turbine systemcomprising: a first region of a tip shroud, the first region disposed inclose proximity to an adjacent first region of an adjacent tip shroud; asecond region of the tip shroud, the second region disposed in closeproximity to an adjacent second region of the adjacent tip shroud; and atemperature sensitive material disposed proximate the second region, thetemperature sensitive material comprising a first volume during a firstoperating condition of the turbine system and a second volume during asecond operating condition of the turbine system, wherein the secondvolume is less than the first volume.
 10. The turbine shroud arrangementof claim 9, wherein the second region and the adjacent second region arein contact during the first operating condition and spaced to provide asecond region gap during the second operating condition.
 11. The turbineshroud arrangement of claim 9, wherein the temperature sensitivematerial comprises a negative thermal expansion material.
 12. Theturbine shroud arrangement of claim 9, wherein the temperature sensitivematerial comprises a shape memory alloy.
 13. The turbine shroudarrangement of claim 9, further comprising a first region gap disposedbetween the first region and the adjacent first region during the firstoperating condition.
 14. The turbine shroud arrangement of claim 13,wherein the first region and the adjacent first region are in contactduring the second operating condition.
 15. The turbine shroudarrangement of claim 9, wherein the adjacent second region comprises thetemperature sensitive material.
 16. The turbine shroud arrangement ofclaim 9, wherein the first operating condition comprises a turbineoperating speed range from about 0% to about 50% of a maximum speed ofthe turbine system.
 17. The turbine shroud arrangement of claim 9,wherein the second operating condition comprises a turbine operatingspeed range from about 30% to about 100% of a maximum speed of theturbine system.
 18. A method of controlling a turbine shroud arrangementcomprising: disposing a first region gap between a first region of a tipshroud and an adjacent tip shroud; reducing a second region gap disposedbetween a second region of the tip shroud and the adjacent tip shroud bydepositing a temperature sensitive material proximate the second region;engaging the second region with the adjacent tip shroud during a firstoperating condition of a turbine system and providing the second regiongap during a second operating condition of the turbine system; andproviding the first region gap during the first operating condition andreducing the first region gap to engage the first region with theadjacent tip shroud during the second operating condition.
 19. Themethod of claim 18, further comprising decreasing a volume of thetemperature sensitive material during increased temperature operatingconditions upon contraction of the temperature sensitive material. 20.The method of claim 18, further comprising depositing the temperaturesensitive material on an adjacent second region of the adjacent tipshroud, the adjacent second region in close proximity with the secondregion of the tip shroud.